The present invention relates to laser processing of a printed circuit board, and more particularly to a laser processing method and a laser processing apparatus suitable for forming holes in a multi-layer printed circuit board having an insulating layer and a conductive layer laminated in multiple layers.
Generally, a multi-layer circuit board is formed by laminating an insulating layer and a conductive layer alternately. Most electronic circuits have come to use widely such multi-layer printed circuit boards which are effective for increasing the mounting density of circuit parts.
Specifically, holes are formed in an insulating layer of a multi-layer printed circuit board, and the holes are filled with solder or conductive paste, which connect adjacent conductive layers in the multi-layer printed circuit board.
Thus, the conventional laser processing apparatus makes holes in the insulating layer by employing laser beam processing technology.
In the laser processing apparatus, laser beams of long wavelength are often used. This is because laser beams of long wavelength are suitable to be absorbed in the insulating layer and easily reflected on the conductive layer. For example, when the insulating layer is a glass epoxy resin with glass fibers in it, and the conductive layer is a copper foil, the processing apparatus selectively removes only the insulating layer by using a carbon dioxide(CO2) laser beam.
When the laser beam opens holes in the resin part exposed in holes of the copper foil of the printed circuit board, the holes of the copper foil of the surface layer are often deviated from the standard positions of holes or the holes of the copper foil are sometimes abnormal in shape and size.
The conventional laser processing apparatus has continued to process the printed circuit board up to the final step, even if there was position deviation of copper foil holes, abnormal hole diameter and hole shape. In such a case, a printed circuit board having small electronic parts mounted on it was not dimensionally correct, so that the printed circuit board did not operate normally and was then scrapped as a defective piece. In the conventional laser processing apparatus, products are checked in the final stage, and defective pieces are sorted out during the final stage. In another case, the conventional laser processing apparatus utilizes an image recognition process or the like, so as to check the hole position, hole diameter and hole shape of the copper foil of the surface layer, before making a hole in the resin part by laser.
Such prior art has the following problems. In the conventional laser processing apparatus, since the printed circuit boards are checked in the final stage, printed circuit boards must be processed completely up to the final stage, even if they have such defects as abnormality in hole position, hole diameter or hole shape of the copper foil and are not usable. As a result, wasteful processing, time, material and energy are spent, and the total manufacturing cost is raised in the conventional process.
In a case of adding a conventional process for checking the hole position, size and shape with an image recognition device before making holes in the resin part by laser processing, such a prior step must be added, and the manufacturing time and cost are increased by this step.
It is, hence, an object of the invention to present a method and apparatus for solving these conventional problems. The invention presents a method and an apparatus for making holes in the resin layer while inspecting the hole position, hole diameter and hole shape of the copper foil of the surface layer, hole by hole, using the laser beam, instead of merely making holes in the resin layer of the printed circuit board.
To solve the problems, the invention presents a laser processing method and apparatus for processing a circuit board including at least two layers, having a conductive layer with a plurality of holes disposed on a surface layer of an insulating layer to be processed by applying a laser beam to an insulating layer corresponding to holes of the conductive layer. In this laser processing method and apparatus, a circuit board is irradiated with a laser beam, and a reflected laser beam is detected, whereby the laser process of the insulating layer corresponding to an abnormal hole in the conductive layer is stopped, if the detected value of the reflected laser beam is an abnormal value outside of a desired value. Also in this laser processing method and apparatus, the insulating layer corresponding to the hole is processed when the detected value of the reflected laser beam conforms to the desired value.